Who, What, Why: How useful is a captured drone?
An American surveillance drone has been captured and filmed in Iran, where experts are apparently examining it. But how much valuable information are they likely to glean?
Pictures broadcast by Iranian television of the stealth RQ-170 Sentinel will have made grim viewing in Washington.
Iran has rejected US calls for its return, and state television says military experts were in the final stages of recovering data.
So how easy is it to extract information from a drone?
It all depends what state the aircraft was in when they recovered it, says Nick Brown, editor-in-chief of Jane's International Defence Review.
"It could have crashed and come apart. The version seen on the video clips could be a reconstruction. But if the aircraft is relatively intact, you could take a fair bit from it."
One thing the Iranians might be doing is testing it with radar in an anechoic chamber, he says, to find its "radar cross-section", which is a measure of how detectable it is. They could also learn from some of the more exotic radar-defeating shaping and materials.
Some parts of the RQ-170 - such as the undercarriage and probably the fly-by-wire avionics and engine - have been taken from existing aircraft, so won't offer much that's new.
"But the real bonanza is likely to be the payload. We don't know what payloads are on there but there's probably signal intelligence, electro-optical sensors and/or a radar.
"The RQ-170 doesn't carry weapons and the two humps on the top of the fuselage are radomes or fairings covering satellite uplinks which send information back from those sensors to the aircraft's control station."
With the RQ-170 itself, the challenge is not so much building it but making it airworthy, says Mr Brown.
"There are complicated algorithms that control the aircraft. Getting a boomerang-shaped object to fly where you want it to fly is hard and only really possible with advanced flight modelling, powerful computers and software.
"So if you don't have that level of information gleaned from the aircraft's onboard hard drive and circuitry you won't easily be able to do anything but build something that's the same shape."
All the control algorithms would be encrypted, so it's not as easy as just reading a hard drive and replicating it, he adds.
Could the Iranians do it?
They are past masters at reverse engineering, says Mr Brown, and they have an awful lot of capability without needing outside help, but sharing the platform with friendly states could offer Tehran substantial political capital.
"Anything is possible and theoretically Iran could copy quite a lot from the basic platform, but it's the control stuff and the avionics that make it usable."
Any form of unmanned technology is potentially very important to Iran, Russia and China, says Elizabeth Quintana, a senior researcher in air power at the Royal United Services Institute.
"But how useful it is depends on how intact the aircraft is, and whether it had any self-destructive, self-disabled mechanisms on board. I suspect it had some but it looks like it's in one piece, from the pictures and video."
It would be capable of taking images and listening in, she says, so there's quite a lot of information on board, not least about the platforms themselves - how they work, how they communicate with satellites and how the Americans operate them. And identifying the materials that enable the drone to absorb radiated energy - rather than reflect it back - would also be very useful.
"I don't know the level of scientific expertise available to Iran but if it's true that Russia and China have sent delegates, then they do have the expertise."